High Strength Fibers of Stereoregular Polystrene

This invention relates to fibers of stereo-regular polystyrene, in particular isotactic and syndiotactic polystyrene. This invention further relates to a process for the preparation of such fibers.

In many industries there is a drive to replace the metals used as structural materials with plastic materials. Plastic materials offer several advantages in that they are frequently lighter, do not interfere with magnetic or electrical signals, and often are cheaper than metals. One major disadvantage of plastic materials is that they are significantly weaker than many metals. To provide plastic structural articles and parts which have sufficient strength for the intended use, it is common to use composite materials which comprise a polymer or plastic matrix with high strength fibers in the plastic or polymer matrix to provide enhanced strength. Examples of composites made using such high strength fibers can be found in Harpell et. al. U.S. Pat. No. 4,457,985 and Harpell et al. U.S. Pat. No. 4,403,012.

A series of patents have recently issued which relate to high strength fibers of polyethylene, polypropylene or co-polymers of polyethylene and polypropylene. Such fibers are demonstrated as being useful in high strength composites. See Harpell et al. U.S. Pat. No. 4,563,392: Kavesh et al. U.S. Pat. No. 4,551,296: Harpell et al. U.S. Pat. No. 4,543,286; Kavesh et al. U.S. Pat. No. 4,536,536; Kavesh et al. U.S. Pat. No. 4,413,110; Harpell et al. U.S. Pat. No. 4,455,273; and Kavesh et al. U.S. Pat. No. 4,356,138. Other polymers which have been used to prepare fibers for composites include polyphenylene sulfide, polyetheretherketone and poly(para-phenylene benzobisthiazole).

The polyethylene and polypropylene fibers although exhibiting excellent modulus and tensile properties, have a relatively low heat distortion temperature and poor solvent resistance. The polyphenylene sulfide, polyetheretherketone, and poly(p-phenylene benzobisthiazole) polymers exhibit excellent heat distortion temperatures and solvent resistance, but are difficult to process and quite expensive.

What are needed are fibers useful in composites which exhibit good solvent resistance and heat distortion properties, are processible, and prepared from materials which have reasonable costs. What are further needed are such fibers with high strength.

The invention is a crystalline fiber comprising syndiotactic polystyrene, or a mixture of syndiotactic polystyrene and isotactic polystyrene. Preferably the fiber is a high strength fiber of isotactic polystyrene and syndiotactic polystyrene wherein the fiber is monoaxially oriented, has a tensile strength of about 10,000 psi or greater, and a modulus of about 1,000,000 psi or greater.

In another aspect the invention is a process for the preparation of fibers of syndiotactic polystyrene, or a mixture of isotactic polystyrene and syndiotactic polystyrene which comprises:

A. contacting syndiotactic polystyrene, or a mixture of isotactic polystyrene and syndiotactic polystyrene with a solvent for the polystyrene at elevated temperatures under conditions such that a homogeneous solution is formed which has sufficient viscosity to be extruded;

B. extruding the solution through an orifice to form a fiber at elevated temperatures;

C. quenching the fiber by passing the fiber through one or more zones under conditions such that the fiber solidifies:

D. removing the solvent for the polystyrene from the fiber: and

E. cooling the fiber to ambient temperature.

In the embodiment where it is desirable to prepare high strength fibers, the fibers are further exposed to the following process steps:

F. heating the fiber to a temperature above the glass transition temperature of the polystyrene:

G. redrawing the fiber to elongate the fiber, maximize crystallinity, and induce monoaxial orientation of the polystyrene in the fiber.

The fibers of this invention exhibit excellent solvent resistance and heat distortion properties, and may be processed and prepared with relative ease. The starting materials used to prepare these fibers can be prepared at a relatively low cost.

The fibers of this invention may be prepared from syndiotactic polystyrene or a mixture of syndiotactic and isotactic polystyrene. Syndiotactic polystyrene is polystyrene whereby the phenyl groups which are pendent from the chain alternate with respect to which side of the chain the phenyl group is pendent. In other words, every other phenyl group is on the opposite side of the chain. Isotactic polystyrene has all of the phenyl rings on the same side of the chain. Note that standard polystyrene is referred to as atactic, meaning it has no stereoregularity, and the placement of the phenyl groups from the styrene with respect to each side of the chain is random, irregular, and follows no pattern.

The fibers of this invention are monoaxially oriented to improve the tensile strength and modulus of the fibers. Preferably the fibers have a tensile strength of 10,000 psi or greater, more preferably 20,000 psi or greater and most preferably 30,000 psi or greater. The fibers of this invention preferably have a modulus of 1,000,000 psi or greater, more preferably 2,500,000 psi or greater, and most preferably 5,000,000 psi or greater. The fibers of this invention may be extruded into any size, shape or length desired. Preferably the fibers of this invention have a heat distortion temperature of 150.degree. C. or greater, more preferably 170.degree. C. or greater and most preferably 190.degree. C. or greater. Preferably the fibers of this invention have a crystalline melting temperature of 200.degree. C. or greater, more preferably 220.degree. C. or greater, and most preferably 240.degree. C. or greater.

Isotactic and syndiotactic polystyrene may be prepared by methods well known in the art. For procedures for the preparation of isotactic polystyrene, see Natta et al., Makromol. Chem., Vol. 28, p. 253 (1958) (relevant portions incorporated herein) by reference. For procedures for the preparation of syndiotactic polystyrene, see Japanese Patent No. 104818 (1987) and Ishihara, Macromolecules, 19 (9), 2464 (1986) relevant portions incorporated herein by reference.

The fibers of this invention may be prepared by a solution spinning process, or melt spin process. In the solution spinning process, the polystyrene is contacted with a solvent for the polystyrene at elevated temperatures. The weight percent of the polystyrene in the solvent should be such that there is sufficient viscosity to extrude the polymer. If the viscosity is too low the fibers coming out of the extruder will have no physical integrity, and if the viscosity is too high the mixture is not extrudable. Preferably the solution has an upper limit on viscosity at the extrusion sheer rate of 1,000,000 poise, more preferably 500,000 poise and most preferably 100,000 poise. Preferably the solution has a lower limit on viscosity at the extrusion sheer rate of 100 poise, more preferably 1,000 poise and most preferably 10,000 poise.

The polystyrene molecular weight should be sufficient such that fibers with reasonable integrity may be formed. The preferred upper limit on molecular weight (Mn) is 4,000,000, with 1,000,000 being more preferred. The preferred lower limit on molecular weight (Mn) is 200,000, with 400,000 being more preferred. Preferably the mixture or solution which is extruded contains up to 40 weight percent of polystyrene, more preferably between about 3 and 30 weight percent of polystyrene and most preferably between 5 and 15 percent polystyrene. The amount of polystyrene which may be dissolved in the various solvents is dependent upon the molecular weight, of the polystyrene as the molecular weight of the polystyrene goes up the weight percent of the polystyrene which may go into solution may be lower.

The temperature at which the materials are contacted is such temperature at which the solution has sufficient viscosity to be extrudable and which does not degrade the polystyrene. The upper temperature is either the degradation temperature of the polystyrene or the boiling point of the solvent, and the lower temperature is that temperature at which the mixture is a single phase liquid. Above about 250.degree. C. the polystyrene undergoes degradation. The upper temperature for the mixing step is preferably about 275.degree. C., and more preferably about 160.degree. C. The lower temperature for the mixing step is preferably 100.degree. C. and more preferably 140.degree. C.

It is desirable, although not essential, that the hot solution of polymer in solvent becomes gelatinous, or more preferably a rigid gel, when it is cooled to lower temperatures. Solutions of syndiotactic polystyrene usually readily form gels, when they are cooled to lower temperatures; isotactic polystyrene solutions may also form gels under such conditions. The ability to form gels from solutions containing both syndiotactic and isotactic polymers can often be controlled to advantage by selection of the proper ratio of each polymer and the selection of the proper solvent. Where a fiber is to be prepared from both syndiotactic polystyrene and isotactic polystyrene the ratio of syndiotactic polystyrene to isotactic polystyrene in the blend is any ratio which gives fiber with structural integrity and is preferably between about 0.1 and 20, more preferably between about 0.75 and 3, most preferably between about 1 and 1.25.

Solvents useful in this invention are those which are a liquid at extrusion temperatures and which dissolve a sufficient amount of the polymer to result in a solution viscous enough to extrude. Preferred solvents include substituted benzenes of the formulas ##STR1## wherein R.sup.1 is alkyl, hydrogen, cycloalkyl, halo, or nitro:

R.sup.2 is alkyl;

R.sup.3 is aryl, alkyl, carboxyaryl, or alkoxy:

a is an integer of from 1 to 3

b is an integer of from 0 to 3

c is an integer of from 1 to 2.

Other preferred solvents include alkyl, cycloalkyl, aryl or aralkyl substituted pyrrolidinones; chloronaphthalenes; hydrogenated and partially hydrogenated naphthalenes; aryl substituted phenols: ethers of the formula ##STR2## wherein R.sup.4 is alkyl, cycloalkyl or aryl: diphenyl sulfone; benzyl alcohol; caprolactam; alkyl aliphatic esters containing a total of from 7 to 20 carbon atoms; alkyl aryl substituted formamides; dicyclohexyl; terphenyls; partially hydrogenated terphenyls: and mixtures of terphenyls and quaterphenyls.

Preferred substituted benzene solvents include o-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, xylene, nitrobenzene, acetophenone, methyl benzoate, ethyl benzoate, diphenyl phthalate, benzil, methyl salicylate, benzophenone, cyclohexyl benzene, n-butylbenzene, n-propylbenzene, phenol, and dimethyl phthalate. Examples of preferred ethers include phenetole (phenyl ethyl ether), diphenyl ether, and anisole. Examples of preferred pyrrolidinone solvents include 1-benzyl pyrrolidinone, 1-cyclohexyl pyrrolidinone, 1-ethyl pyrrolidinone, 1-methyl pyrrolidinone, and 1-phenyl pyrrolidinone. More preferred pyrrolidinone solvents include the alkyl and cycloalkyl substituted pyrrolidinones. Even more preferred pyrrolidinone solvents include 1-cyclohexyl pyrrolidinone, 1-ethyl pyrrolidinone and 1-methyl pyrrolidinone. Preferred ether solvents include anisole and diphenyl ether. Preferred hydrogenated naphthalene solvents include decahydronaphthalene (decalin) and tetrahydronaphthalene (tetralin). Examples of terphenyls and partially hydrogenated terphenyls preferred include partially hydrogenated terphenyls, available from Monsanto under the tradename Therminol.RTM. 66: mixed terphenyls and quaterphenyls, available from Monsanto under the tradename Therminol.RTM. 75; and mixed terphenyls available from Monsanto under the Santowax.RTM. R tradename.

More preferred aliphatic esters are those methyl aliphatic esters with a total of from 10 to 14 carbon atoms, with methyl laurate being most preferred.

More preferred solvents include 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1-ethyl-2-pyrrolidinone, 1-methyl pyrrolidinone, 1-cyclohexyl-2-pyrrolidinone, acetophenone, anisole, benzil, benzophenone, benzyl alcohol, caprolactam, decahydronaphthalene, tetrahydronaphthalene, diphenyl ether, ethyl benzoate, methyl salicylate, orthodichlorobenzene, mixed terphenyls and partially hydrogenated terphenyls. Even more preferred solvents include 1,2,3-trichlorobenzene, 1-ethyl-2-pyrrolidinone, anisole, tetrahydronapthalene, and ortho-dichlorobenzene. The most preferred solvent is ortho-dichlorobenzene.

Once the mixture has been prepared it is extruded through a die of a desired shape, usually a circular die, into the form of a fiber. The extrusion is performed at elevated temperatures, the upper limit on the temperature is the lower of the boiling point of the solvent or the degradation temperature of the polystyrene. The lower limit on temperature is the lowest temperature at which the mixture is a single phase homogeneous solution and extrudable. Preferred upper limit on temperature is 250.degree. C., with 160.degree. C. being most preferred. The preferred lower limit on temperature is 100.degree. C. with 140.degree. C. being most preferred. The temperature used to extrude the material is dependent upon the polymer concentration and molecular weight of the polystyrene, as the polymer concentration goes up the temperature necessary to extrude the fibers goes up.

From the extruder the fiber is passed through one or more quench zones. Such quench zones may be gaseous quench zones, liquid quench zones or a combination thereof. In the quench zones the fiber is cooled, solidified and drawn down. In a gaseous quench zone the fiber is passed through a gaseous zone, such zone may be at a temperature of between 0.degree. and 100.degree. C., preferably the temperature is ambient temperature. The length of the gaseous quench zone is as short as possible, preferably between 0 and 18 inches more preferably between 0 and 6 inches. The preferred gas is air. In a liquid quench zone the fiber is cooled and solidified, and a portion of the solvent may be removed from the fiber at this time. The liquid which may be used for the liquid quench is a liquid which is a solvent for the polystyrene solvent but which does not dissolve the polystyrene. Preferred quench zone materials include water, lower alcohols, halogenated hydrocarbons, and perhalogenated carbon compounds. Perhalogenated carbon compounds are materials with a carbon backbone wherein all of the hydrogen atoms have been replaced with halogen atoms. Preferred quench materials include water and lower alcohols with lower alcohols being most preferred. Preferred lower alcohols are C.sub.1-4 alcohols. The lower limit on the temperature of a liquid quench zone is that temperature at which the quench material freezes. The upper limit on the temperature of a liquid quench zone is the lower of the boiling point of the solvent, or that temperature above which the fiber does not undergo solidification when in contact with the quench material. Preferably the upper limit on temperature is 80.degree. and more preferably 30.degree. C. Preferably the lower limit on temperature is 0.degree. C.

In a preferred embodiment, the quench zone comprises an air quench zone and a liquid quench zone. In the air quench zone the fiber undergoes partial solidification and loss of some of the solvent, and in the liquid quench zone solidification is completed and more of the solvent is removed. During the quench period the fiber is also drawn down. Preferably the lower limit on the draw down is from about 10:1, more preferably about 50:1. Preferably the upper limit on the draw down is about 100:1. Drawing down means the fibers are stretched such that the cross sectional area of the fiber is smaller at the end of the process and the draw down ratio is the ratio of the beginning cross sectional area to the final cross sectional area. The residence time of the fiber in a liquid quench bath is preferably greater or equal to 1 second, more preferably between about 1 and 10 seconds.

After quenching the fiber, the fiber is subjected to a leach step wherein the remainder of the solvent in the fiber is removed. The material in which the leaching occurs is a material which is a solvent for the polystyrene solvent and which does not dissolve the polystyrene. The materials which may be used in the leach are the same materials which may be used in a liquid quench. Temperatures of the leach bath are those temperatures at which the remaining solvent in the fibers is substantially removed. Preferably the leaching occurs at ambient temperatures, between about 20 and about 40.degree. C. more preferably between about 20 and 30.degree. C. The residence time in the leach bath is sufficient time such that the solvent is substantially removed. Preferably the residence time and leach bath is greater then 30 seconds, more preferably between about 1 min. and 48 hours and most preferably between about 1 min. and 2 hours. The leach may either be performed in a continuous on-line process, or may be performed in a batch fashion. The residence time is dependent upon the particular solvent, the fiber size, and the kinetics for removing the solvent from the fiber.

After forming the fiber and removing the solvent the fiber is then allowed to cool to ambient temperature.

When it is desired to improve the strength of the fiber, the fiber is reheated to a temperature at which the fiber can be redrawn. It is in the redraw process that the fiber is oriented such that the fiber has monoaxial orientation. The fiber is heated to a temperature between its glass transition temperature and its melting point. Preferable upper temperatures are 280.degree. C. or below and more preferably 270.degree. C. or below. Preferable lower temperatures are 150.degree. C. or above and more preferably 250.degree. C. or above. Thereafter the fiber is redrawn by stretching the fiber with tension; this is usually performed by running the fibers over a set of godets wherein the latter godets are going at a much faster rate than the earlier godets. The fiber is elongated at a ratio of between about 1.5:1 and about 10:1. Preferably the rate of elongation is 1 foot per minute or less. The redraw occurs while the fiber is at or near the temperature to which it was preheated. The fiber may be drawn in one or more stages with the options of using different temperatures, draw rates, and draw ratios in each stage.

In another embodiment, the fibers of this invention may be prepared by a melt spin process. In the melt spin process, the neat polymer is heated to a temperature between its crystal melting point and the temperature at which the polymer undergoes degradation. The particular temperature depends upon whether syndiotactic polystyrene or a mixture of isotactic and syndiotactic polystyrene is used. Generally the crystal melting temperature of isotactic polystyrene is somewhat lower than that of syndiotactic polystyrene. The neat polymer is first melted to a temperature at which the material has sufficient viscosity to extrude. The viscosity should be high enough such that the fiber extruded has integrity yet not so high that the polymer is too viscous to be extruded. The preferred upper limit on viscosity is 1.times.10.sup.6 poise, with 5.times.10.sup.5 poise more preferred, and 1.times.10.sup.5 poise most preferred. The preferred lower limit on viscosity is 1.times.10.sup.2 poise, with 1.times.10.sup.3 poise more preferred, and 1.times.10.sup.4 poise most preferred. The molecular weight of the polystyrene should be such that fibers of reasonable integrity may be formed. The preferred upper limit on molecular weight (Mn) is 4.times.10.sup.6, with 3.times.10.sup.6 being more preferred, and 2.times.10.sup.6 most preferred. The preferred lower limit on molecular weight is 2.times.10.sup.5, with 5.times.10.sup.5 being more preferred and 1.times.10.sup.6 most preferred. Preferably the polymer is melted to a temperature of between about 270.degree. and about 300.degree. C. Thereafter the fiber is extruded at such temperatures. Preferred extrusion temperatures are between about 270.degree. and 300.degree. C. Thereafter the fiber is passed through a quench zone. The quench zone may be either a gaseous quench zone or a liquid quench zone. For a melt extrusion generally an air quench zone is preferred. The air quench zone is generally long enough to quench and solidify the fiber. Such zone is preferably between about 1 and 6 feet. The temperature of the quench zone can be any temperature at which the fiber undergoes a reasonable rate of cooling and solidification. The preferred lower temperature is about 0.degree., most preferably about 20.degree.. The preferred upper temperature is about 100.degree. C., most preferably about 50.degree. C. During the quench period the fiber is drawn down from between about 10:1 to 100:1. After the quench period, the fiber is allowed to cool to ambient temperatures. To prepare high strength fibers, the fiber is thereafter heated to between the T.sub.g of the polymer and the melting point of the polymer. The preferred upper temperature is about 280.degree. C. with 270.degree. C. being most preferred. The preferred lower temperature is preferably 150.degree. C., and more preferably 160.degree. C. While the fiber is still between its T.sub.g and its melting temperature the fiber is redrawn as described previously. The slower the rate the better the orientation and stronger the fiber will be. Generally the elongation will be up to a ratio of 4 to 1.

The fibers of this invention as discussed before can be incorporated into composites. The methods for such incorporation and the composites in which the fibers can be used in are well known to those skilled in the art.

The following examples are included for illustrative purposes only and are not intended to limit the scope of the invention or the claims. Unless otherwise stated all parts and percentages are by weight.

6% isotactic polystyrene, 6% syndiotactic polystyrene, and 88% o-dichlorobenzene are mixed at 120.degree. C. for 10 minutes. The resulting mixture, containing dissolved and partially dissolved polymer, is added to the melt pot of a pot extruder. This mixture is then heated to 170.degree. C. and stirred for one hour under a nitrogen atmosphere. The mixture is then extruded at 110.degree. C. through a 1.0 mm diameter spinnerette into a methanol bath to form a gel fiber. The fiber is collected and extracted in methanol for 24 hours to remove the o-dichlorobenzene. The extracted fiber is stretched 350% at 100.degree. C. to produce a fiber with a tensile strength of 10,700 psi and a modulus of 1,300,000 psi with an elongation of 1.9%.

7% isotactic polystyrene, 3% syndiotactic polystyrene, and 90% o-dichlorobenzene are mixed at 120.degree. C. for 10 minutes. The resulting mixture, containing dissolved and partially dissolved polymer, is added to the melt pot of a pot extruder. This mixture is then heated to 170.degree. C. and stirred for one hour under a nitrogen atmosphere. The mixture is then extruded at 110.degree. C. through a 1.0 mm diameter spinnerette into a methanol bath to form a gel fiber. The fiber is collected and extracted in methanol for 24 hours to remove the o-dichlorobenzene. The extracted fiber is stretched at a ratio between 3:1 and 4:1 at 150.degree. C. to produce a fiber with a tensile strength of 23,000 psi and a modulus of 500,000 psi. The final elongation is 25%.

3.5% isotactic polystyrene, 1.5% syndiotactic polystyrene, and 95% o-dichlorobenzene are mixed at 120.degree. C. for 10 minutes. The resulting mixture, containing dissolved and partially dissolved polymer, is added to the melt pot of a pot extruder. This mixture is then heated to 170.degree. C. and stirred for one hour under a nitrogen atmosphere. The mixture is then extruded at 130.degree. C. through a 1.0 mm diameter spinnerette into a methanol bath to form a gel fiber. The fiber is collected and extracted in methanol for 24 hours to remove the o-dichlorobenzene. The extracted fiber is stretched 900% at 150.degree. C. to produce a fiber with a tensile strength of 14,000 psi and a modulus of 1,300,000 psi.

5% isotactic polystyrene, 5% syndiotactic polystyrene, and 90% o-dichlorobenzene are mixed at 120.degree. C. for 10 minutes. The resulting mixture, containing dissolved and partially dissolved polymer, is added to the melt pot of a pot extruder. This mixture is then heated to 170.degree. C. and stirred for one hour under a nitrogen atmosphere. The mixture is then extruded at 110.degree. C. through a 1.0 mm diameter spinnerette into a methanol bath to form a gel fiber. The fiber is collected and extracted in methanol for 24 hours to remove the o-dichlorobenzene. The extracted fiber is stretched 300% at 130.degree. C. to produce a fiber with a tensile strength of 29,000 psi and a modulus of 2,700,000 psi with a final elongation of 2.2%.

7% syndiotactic polystyrene, and 93% o-dichlorobenzene are mixed at 120.degree. C. for 10 minutes. The resulting mixture, containing dissolved and partially dissolved polymer, is added to the melt pot of a pot extruder. This mixture is then heated to 170.degree. C. and stirred for one hour under a nitrogen atmosphere. The mixture is then extruded at 110.degree. C. through a 1.0 mm diameter spinnerette into a methanol bath to form a gel fiber. The fiber is collected and extracted in methanol for 24 hours to remove the o-dichlorobenzene. The extracted fiber is stretched 200% at 150.degree. C. to produce a fiber with a tensile strength of 10,000 psi and a modulus of 1,300,000 psi.

Syndiotactic polystyrene, with a molecular weight of 300,000 M.sub.w, is placed in the heating zone of an extruder and heated to 250.degree. C. The polystyrene is extruded at 250.degree. C. through a 1.0 mm diameter spinnerette into an air quench zone. The fiber after quenching is taken up and allowed to cool to ambient temperature. The fiber exhibits a tensile strength of 15,000 psi, and a modulus of 1,200,000 psi with a final elongation of 5.6%.

Syndiotactic polystyrene, with a molecular weight of 700,000 M.sub.w, is placed in the heating zone of an extruder and heated to 260.degree. C. The polystyrene is extruded at 260.degree. C. through a 1.0 mm diameter spinnerette into an air quench zone. The fiber after quenching is taken up and allowed to cool to ambient temperature. The fiber is redrawn 100% at 180.degree. C. The fiber exhibits a tensile strength of 19,000 psi, and a modulus of 830,000 psi with a final elongation of 4.1%.

Syndiotactic polystyrene, with a molecular

weight of 700,000 M.sub.w, is placed in the heating zone of an extruder and heated to 260.degree. C. The polystyrene is extruded at 260.degree. C. through a 1.0 mm diameter spinnerette into an air quench zone. The fiber after quenching is taken up and allowed to cool to ambient temperature. The fiber is redrawn 160% at 280.degree. C. The fiber exhibits a tensile strength of 15,000 psi, and a modulus of 950,000 psi with a final elongation of 3.9%.

Syndiotactic polystyrene, with a molecular weight of 800,000 M.sub.w, is placed in the heating zone of an extruder and heated to 275.degree. C. The polystyrene is extruded at 275.degree. C. through a 1.0 mm diameter spinnerette into an air quench zone. The fiber after quenching is taken up and allowed to cool to ambient temperature. The fiber exhibits a tensile strength of 10,000 psi, and a modulus of 410,000 psi with a final elongation of 3.7%.

Syndiotactic polystyrene, with a molecular weight of 800,000 M.sub.w, is placed in the heating zone of an extruder and heated to 275.degree. C. The polystyrene is extruded at 275.degree. C. through a 1.0 mm diameter spinnerette into an air quench zone. The fiber after quenching is taken up and allowed to cool to ambient temperature. The fiber is redrawn 50% at 280.degree. C. The fiber exhibits a tensile strength of 8,000 psi, and a modulus of 470,000 psi with a final elongation of 2.1%.

Syndiotactic polystyrene, with a molecular weight of 3,000,000 M.sub.w, is placed in the heating zone of an extruder and heated to 300.degree. C. The polystyrene is extruded at 300.degree. C. through a 1.0 mm diameter spinnerette into an air quench zone. The fiber after quenching is taken up and allowed to cool to ambient temperature. The fiber exhibits a tensile strength of 12,000 psi, and a modulus of 450,000 psi with a final elongation of 6.3%.

Syndiotactic polystyrene, with a molecular weight of 3,000,000 M.sub.w, is placed in the heating zone of an extruder and heated to 300.degree. C. The polystyrene is extruded at 300.degree. C. through a 1.0 mm diameter spinnerette into an air quench zone. The fiber after quenching is taken up and allowed to cool to ambient temperature. The fiber is redrawn 50% at 280.degree. C. The fiber exhibits a tensile strength of 14,000 psi, and a modulus of 700,000 psi with a final elongation of 3.8%.

Mixtures consisting of approximately five weight percent polymer in various organic compounds are prepared in two dram-capacity glass vials that are subsequently sealed with aluminum foil liners. The mixtures are weighed to a precision of one milligram. The vials are placed in an air-circulating oven at about 125.degree.-140.degree. C. Dissolution behavior is observed by transmitted light at close range from an AO universal microscope illuminator at progressively increasing temperatures until complete dissolution is observed, until the boiling point of the solvent is closely approached, or until 300.degree. C. is reached (the approximate ceiling temperature of the polystyrene). The temperature is increased in about 25.degree. C. increments. The mixtures are allowed to remain at a given temperature for at least about 30 minutes before the temperature is increased further. The hot mixtures are cooled to room temperature; their appearance is noted after they are allowed to stand undisturbed overnight at room temperature. The results are compiled in Table I. The polymer noted as "IPS42" refers to a sample of isotactic polystyrene with a viscosity average molecular weight in excess of 2.6.times.10.sup. 6 daltons and contains about 9.4% atactic polystyrene (i.e. polymer extractable with hot methyl ethyl ketone). The polymer noted as "SYNDIO2" is a sample of syndiotactic polystyrene with a weight-average molecular weight of about 5.6.times.10.sup.5 daltons. The polymer noted as "SYNDIO" is a sample of syndiotactic polystyrene with a lower molecular weight.